Air heater with solid fuel and fluid fuel burning furnaces arranged in tandem



Oct. 10, 1950 R. F. CRAWFORD 2,525,400 AIR HEATER WITH SOLID FUEL AND FLUID FUEL BURNING FURNACES ARRANGED IN TANDEM Filed June 26, 1946 Patented Oct. 10, 1950 AIR HEATER WITH SOLID FUEL AND FLUID FUEL BURNING FURNACES ARRANGED IN TANDEM Raymond F. Crawford, Steubenville, Ohio Application June 26, 1946, Serial No. 679,406

6 Claims.

This invention relates generally to improvements in hot air furnaces for domestic use and more particularly to a tandem hot air furnace of forced circulation type and arranged to burn two different kinds of fuel.

The principal object of this invention is the provision of a domestic heating furnace of the forced circulating type having a fluid fuel heat exchanger and a solid fuel heat exchanger in tandem.

Another object is the provision of a domestic heating furnace of the forced circulating type having a dual source of heat in tandem.

Another object is the provision of a domestic heating furnace having dual source of heat, one of solid fuel and the other of fluid fuel, the latter of which is arranged to automatically supply heat when the former fails to supply heat.

Another object is the provision of a coal furnace having a plenum chamber arranged to receive a fluid fuel heat exchanger to be operated selectively or simultaneously in tandem.

Other objects and advantages will appear hereinafter in the following description and claims.

A practical embodiment illustrating the principles of this invention is shown in the accompanying drawings wherein:

Figure 1 is a view in vertical section of the furnace comprising this invention.

Figure 2 is a perspective view of the plenum chamber with parts broken away to illustrate the fluid fuel heat exchanger.

Figure 3 is a diagrammatical view showing a circuit for controlling the operation of the furnace comprising this invention.

Referring to Figure 1, l represents a typical hot air coal furnace comprising an ash pit grate I2, fire bowl I3, furnace head l4, and radiator l5 which is connected to the top of the furnace by a collar drum l6. The lower end of the radiator I5 is in turn connected by thepipe I! to the flue Hi. The flue pipe l'l extends outwardly through the furnace jacket or casing I9 to the flue and preferably on the side or at the rear of the furnace whichever is most convenient for the specific installation.

A circulating duct connects the fan chamber 2| to the interior of the furnace casing I!) at a point adjacent the bottom of the radiator I5. The fan chamber 2| is provided with a circulating fan 22 arranged to be driven by the motor 23. A duct 24 is connected to the top of the fan chamber 2| and is arranged to receive air from the various rooms of the dwelling and direct it through the cleaning screens 25 to the fan chamber 2| for the purpose of cleaning the air circulated in the heating system.

A plenum chamber or bonnet 26 is mounted on top of the furnace casing IS. The plenum chamber 26 has no bottom and opens to its full extent into the upper end of the casing |9 and is arranged to receive the air that is circulated by the fan 22 which passes up around the furnace drum and the radiator I5 where it absorbs heat. The heated air travels up through the plenum chamber 26 to the top thereof where it is distributed through the ducts 21 to different parts of the dwelling.

The plenum chamber 26 is provided with greater head room than the ordinary furnace bonnet for the purpose of receiving the fluid fuel heat exchanger 28. This heat exchanger comprises a combustion chamber 29 which preferably extends the full width of the plenum chamber 26 and is provided with a burner 30 at the lower end thereof. This combustion chamber may be constructed with its inner wall sloping as indicated at 3| which wall is provided with a series of uniformly spaced openings for receiving the lower end of the heat exchanger tubes 32. The tubes 32 may be of any desired shape although they are preferably made elliptical with the long axes of the ellipse disposed in spaced parallel planes. Each of the heat exchanger tubes 32 is spaced from one another and from the sides of the plenum chamber to allow for the circulation of air therethrough. It is preferable to restrict the spacing of the tubes so as to produce a slight resistance to the flow of air through the heat exchangers. This spacing may be a fraction of the short dimension of the ellipse of the tubes or a fraction of the diameter of the tubes if they are.

cylindrical in form.

The upper end of the heat exchanger tubes 32 are connected with the header 33 which is preferably inthe form of a rectangular box extending the full width of the plenum. One end of the header 33 is provided with a clean out port 34 which opens through the wall of the plenum chamber 26 and the other end is provided with a flue pipe 35 arranged to be connected to the flue I8 for the purpose of withdrawing the products of combustion from the header.

A combustion chamber door 36 is hinged at its upper end to the wall of the plenum chamber, as shown at 31, to provide access to the Whole of the combustion chamber 29. This door may be provided with a screen 38. at the bottom thereof for the purpose of admitting secondary air to the combustion chamber 29 and also. for visually turn is connected to the gas regulator 4| which is supplied with fuel from any suitable source through the pipe 42. A pilot light 43 is connected to the supply side of the fuel valve for feeding the pilot 44 which is preferably disposed in the central portion of the burner 30. pilot device 45 is arranged to operate the fuel valve 46 disposed in the gas line between the fuel valve 40 and the regulator 4| for shutting off the fuel to the burner 3!] if for any reason the pilot light ceases to burn. Any well-known type of safety pilot device may be employed for this purpose but it is believed best to employ valves that must be reset manually.

Referring to Figure 3, the source of electric current is assumed to bethat of alternating current and is indicated by the line wires 47 and 48 which are connected to the lines 5!! and 5! through the double pole snap switch 52.

The line circuit 5!), 5! is connected to the primary 53 of the step down transformer 54, one end of the secondary 55 of which is connected by the wire 58 to the two thermostats 51 and 58 that are positioned at any suitable location in the dwelling. The thermostat 5'? has a pair of con tacts Gil and 6! which may be set for the high and low temperature setting, between which limits the draft 62 and check as are regulated on the coal fu-rna-ceiii. are connected to the motor lit by the wires 65 and 56. The motor 64 is arranged to turn through 180 to open the draft 6-2 and close the check t3 by means of the cable 81 when contact 6! is energized for the purpose of increasing the temperature of the dwelling by increasing the speed of solid fuel consumption. When the dwelling reaches the proper temperature the thermostat 51 engagesv the contact 39 to energize the motor 64 through the wire 55- to operate through another phase of 180 to close the damper 62 and open the check 63. The circuit of the motor 64 is completed through the return wire 68 to the other side of the transformer secondary 55. The motor 85 is arranged to work only throughlBi) for each function and rotates The contacts 6!] and Bi 1 A safety this circuit is de-energized the valve 65 closes and only in one direction. At the end of each move merit the motor resets the circuit for the purpose of receiving the opposite function.

When the plenum chamber 26 reaches a pre determined temperature due to increased heat from either furnace thebimetallic thermostat 1D in this plenum chamber closes a circuit from the wire 59, thermal element it, wire "H to motor 23 and return through the wire 5!. The motor 23 will continue to" operate the fan 22 until the temperature of the plenum chamber 26 is 'cooledto' a predetermined temperature which, ordinarily is lower than the temperature at which the thermal elementv ll! initiates this circuit. The thermal: element ill is usually shunted by a switch such as the snap switch 12 for the purpose of'manually operating the motor 23 to drive the fan 22. V

Thethermostat 5,8 in the dwelling controls the 4 booster furnace. This thermostat may be set to energize the gas valve 40 if the solid fuel furnace does not supply the heat called for by the thermostat 5?. Thus, the thermostat 58 isto supply heat at a temperature slightly below that of the thermosat 57 which controls the solid fuel burning furnace draft. The circuit is made from the wire-5B, through the thermostat 58,, the contact '13, the wire 14, thecoil E5 of the valve All, and return through the wire 68. Upon energizing the coil 75 the valve 40 is opened and gas flows to the burner 30 where it is ignited b the pilot 44.

If the pilot lighte is not burning the thermal element 45 opens the circuit from the wire 56, the contact 75, the element 45, the wire T7, the coil is and return through the wire 68. When the gas flow is shut off to the furnace and it must be manually reset to again function. If there is an interruption in the current supply both valves 55, and as will close. The safety pilot 45 can be arranged to interrupt the circuit of the valve 53 rather than to provide the additional valve 45. Both of these arrangements are be lieved to be well known in the art.

1. In a domestic heating furnace, the combination of means defining a combustion chamber having a flue connection for the discharge of the products of combustion, means defining an en'- closed hot air chamber surrounding tllGCOlfIlbllS- tion chamber but not in' communication therewith, means defining a plenum chamber supported above the hot air chamber and arranged to receive all of the air passing upwardly through the hot air chamber, duct means connected with the plenumchamber for conveying air therefrom for distribution, a second furnace within the plenum chamber in spaced relation ata higher elevation and vented to the fine. and

means for conducting air to the bottom of the hot air chamber for the purpose of circulating the air through the, furnaces in tandem.

2. In a domestic heating furnace, the combination means defining a combustion h m er having a flue connection for the discharge of the products of combustion, m ans defining an enclosed hot air chamber surrounding the com-- bustion chamber but not in communication theerwith, means defining a plenum. chamber supported above the hot air chamber and arranged to receive all of the air passing upwardly through the hot air-chamber, duct means c nnected :with the top of the plenum chamber for conveying air therefrom for distribution, second furnace withinv the plenum chamber in paced'relaiiion above he first furna e and etween the hot air chamber and the duct means and comprising ,means defining a combustion chamber having heat exchange tube means with one end connected thereto and the other end connected to a header. at a higher elevation and vented to, the flue, and means for conducting air to the bottom'of the hot air chamber for the purpose of circulating the air through the furnac snt ndem:

3. In a domestic heating furnacana combine: tiontion of means defininga combustion chamber having algflue connection for the discharge of the products 0f1combllSl3i0n, means defining an enclosed hot air chamber surrounding the combustion chamber but not in communication therewith, means defining a plenum chamber supported above the hot air chamber and arranged to receive all of the air passing upwardly through the hot air chamber, duct means con nected with the top of the plenum chamber for conveying air therefrom for distribution, a second furnace within the plenum chamber in spaced relation above the first furnace and between the hot air chamber and the duct means and comprising means defining a combustion chamber having heat exchange tube means with one end connected thereto and the other end connected. to a header at a higher elevation and vented to the flue, return duct means to conduct air to the bottom of the hot air chamber, and means for forcing the circulation of air through the hot air chamber, the plenum chamber and the distributing duct means.

4. In a domestic heating furnace, the combination of means defining a solid fuel combustion chamber vented to a flue, for the dis-charge of the products of combustion, means defining an enclosed hot air chamber surrounding the combustion chamber but not in communication therewith, means defining a rectangularly shaped plenum chamber supported in spaced relation above the solid fuel combustion chamber and its hot air chamber and arranged to receive all of the air passing upwardly through the hot air chamber, means defining a combustion chamber extending across the bottom of the plenum chamber at one end thereof and containing a fluid fuel burner, a header extending across the opposite end of the plenum chamber at a higher elevation than the combustion chamber and connected to the flue, a plurality of heat exchange tubes extending between the combustion chamber and the header, duct means connected with the plenum chamber above the heat exchange tubes, and means for conducting air to the bottom of the hot air chamber for the purpose of circulating the air through the furnace in tandem.

5. In a domestic heating furnace, the combination of means defining a solid fuel combustion chamber vented to a flue for the discharge of the products of combustion, means defining an enclosed hot air chamber surrounding the combustion chamber but not in communication therewith, means defining a rectangularly shaped plenum chamber supported in spaced relation above the solid fuel combustion chamber and its hot air chamber and arranged to receive all of the air passing upwardly through the hot air chamber, means defining a combustion chamber extending across the bottom of the plenum chamber at one end thereof and containing a iuel burner, a header extending across the opposite end of the plenum chamber at a higher elevation than the combustion chamber and connected to the fiue, the adjacent sides of the combustion chamber and the header defining a plurality of spaced aligned openings, heat exchange tubes connected to said openings to provide com munication between the combustion chamber and the header and offer a resistance to the flow of air through the plenum chamber, duct means connected with the plenum chamber above the heat exchange tubes, and means for conducting air to the bottom of the hot air chamber for the purpose of circulating the air through the furnace in tandem.

6. In a domestic heating furnace, the combination of means defining a combustion chamber having a flue connection for the discharge of the products of combustion, means defining an enclosed hot air chamber surrounding the combustion chamber but not in communication therewith, means defining a plenum chamber supported above the hot air chamber and arranged to receive all of the air passing upwardly through the hot air chamber, duct means connected with the plenum chamber for conveying air therefrom for distribution, a thermostat arranged to control the burning of fuel in said combustion chamber, a second furnace within the plenum chamber in spaced relation above the first furnace and comprising means defining a combustion chamber having heat exchange tube means with one end connected thereto and the other end connected to a header at a higher elevation and vented to the flue, a thermostat arranged to control the burning of fuel in the second furnace, and set to energize the second furnace to supply heat at a temperature slightly below that of the first thermostat, and means for conducting air to the bottom of the hot air chamber for the purpose of circulating the air through the furnaces in tandem.

RAYMOND F. CRAWFORD.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 776,053 Gifford Nov. 29, 1904 948,133 Coyle Feb. 1, 1910 971,938 Thomas Oct. 4, 1910 990,755 Lembke Apr. 25, 1911 1,636,173 Diehm July 19, 1927 1,877,421 Munkel Sept. 13, 1932 

